1. Field of the Invention
This invention relates to improvements in heart pacers, and more particularly to improvements in heart pacers of the type which are externally programmable or controllable by digital circuitry to exhibit variable operating parameters, and, still more particularly, to circuit means for remotely indicating the digital states controlling the parameters of an implantable heart pacer.
2. Description of the Prior Art
For some time, efforts have been made to provide a fully implantable heart pacer of which selected operating parameters can be externally controlled after the pacer has been implanted into the body of a patient. Parameters of interest may include the stimulation pulse amplitude, width, and rate, the refractory period, the sensitivity to naturally occurring heart pulses, the mode, i.e., asynchronous, synchronous, demand and so forth.
Typical heart pacers having such variable parameters are shown in U.S. Pat. Nos. 3,805,796 and 3,833,005. In addition, patent application Ser. No. 663,372 filed Mar. 3, 1976 by Robert A. Walters, and assigned to the assignee of the present invention discloses a heart pacer having variable operating parameters which are controlled by digital circuitry responsive to externally applied magnetic pulses. Said patent application Ser. No. 663,372 has been allowed, and is incorporated herein by reference.
In the circuits of the prior art, when a change in the stimulation pulse rate is made, the change is usually readily observable upon an electrocardiographic device connected to the patient. However, many of the other parameters which can now be externally controlled, such as the sensitivity of the pacer, the refractory period of the pacer, and so forth, are not so readily observable. In fact, confirmation of the programmed change in the pacer may be impossible without the actual removal of the pacer from the patient. In addition, as the number of parameters which can be changed in a single pacer increases, the number of combinations of controlled data becomes cumbersomely large to confirm the change of all but the most important parameters. To illustrate, for example, if a pacer has eight selectable stimulation rates, two widths, four amplitudes, two modes, two refractory periods and four sensitivities, then there are 1,024 combinations which can be programmed. Consequently, what is needed is a means for simply determining or confirming that an implanted heart pacer has been properly programmed.